1. Field of the Invention
The present invention relates to image sensors for capturing images of fringes, and more specifically, to an image sensor that can be configured more easily than the conventional sensors and can perform high-speed detection. The present invention also relates to attitude detectors for detecting the attitude of an irradiated body by using the image sensor. The present invention further relates to contact probes and multi-sensing probes using the attitude detector.
2. Description of the Related Art
A conventional attitude detector for optically detecting the attitude of an irradiated body uses an interferometer to generate interference fringes and detects images of the fringes by using an imaging element (image sensor).
Attitude Detector
One general attitude detector using a Michelson interferometer will be described. A beam splitter splits laser light emitted from a laser light source into a reference beam and a measurement beam. The reference beam hits a reference mirror, and the measurement beam hits a reflecting surface formed on the irradiated body. The beam splitter recombines the beams reflected from the reference mirror and the irradiated body to cause interference. The resulting interference fringes are captured by an image sensor. When the attitude of the irradiated body changes, the corresponding change appears in the captured image of the interference fringes. By detecting the change in the fringe image, the change in the attitude of the irradiated body can be determined.
Image Sensor
As the image sensor used in the conventional attitude detector, a position sensor device (PSD) or an area image sensor is generally used to capture two-dimensional images such as interference fringe images.
Although it allows high-speed detection, the PSD detects the centroid value of the amount of light. The PSD is suitable for detecting light in spots but is not suitable for detecting fringes such as interference fringes. Because of its limited ability to detect the attitude (translation or rotation) of the reflecting surface of the irradiated body, complicated signal processing needs to be performed.
The area image sensor has many pixels (light receiving elements) arranged two-dimensionally on a light receiving plane and is formed of a charge-coupled device (CCD) or a complementary metal-oxide semiconductor (CMOS). Since each pixel can detect the amount of light received, this sensor is suitable for detecting fringe images and is sufficiently capable of detecting the attitude of the reflecting surface of the irradiated body. The CMOS type is capable of performing faster detection than the CCD type. Area image sensors capable of even faster detection for high-speed cameras have come into the market in recent years. Nevertheless, the detection speed of any area image sensor is far slower than that of a PSD.
Disclosed in Patent Literature 1 is a contact probe for detecting the attitude of a movable body (stylus) based on values detected in interference fringe detection performed by using one straight row of pixels (line image sensor) to improve the interference fringe detection speed.
The line image sensor is capable of performing high-speed detection generally at a sampling frequency (frame rate) of several tens of kilohertz. By using the line image sensor, the response of the attitude detector can be improved. The detection speed is about 1000 times higher than the sampling frequency of the CCD, which is a representative example of the area image sensor, and is also significantly higher than that of the PSD. Therefore, the attitude detector using the line image sensor disclosed in Patent Literature 1 can realize a highly functional detector with high resolution, high stability, fast response, and the like.